1. Field of the Invention
The present invention generally relates to a starter having an overrunning clutch used for starting internal combustion engines.
2. Related Art
In the conventional starter with epicycle gear reduction mechanism disclosed in Japanese Patent Laid-open Ser. No. 52-19528, an overrunning clutch is set between the outer circumference surface of an internal gear of an epicycle gear reduction mechanism and inner circumference surface of casing that acts as the fixing side to store the epicycle gear reduction mechanism.
With the conventional structure explained above, the advantages include that the overrunning clutch is set on the outer circumference of the epicycle gear reduction mechanism so the axial direction space used by the overrunning clutch is not required, the dead space is small, and increased manufacturing costs caused by an increase in weight are low. Furthermore, even if a drive transmission portion with a large diameter is required for the high-load overrunning clutch, the outer circumference of the epicycle gear reduction mechanism can be used.
With the conventional structure explained above, however, rollers bite, in the small narrow direction, into wedge-shaped spaces formed between a cam-shaped groove set on the inner circumference of a clutch outer and inclined circumferentially and an outer circumference of a clutch inner that is the outer circumference of the internal gear. This causes a wire contact, and the torque is conveyed with the frictional force generated there. Therefore, the clutch outer member and clutch inner member must be able to withstand an extremely large stress that occurs on the contact surface with the rollers. A high-strength metal material (e.g., heat treated iron and steel material) must be used for the clutch inner member and clutch outer member. Thus, it is not possible to reduce the operational sound when the internal gear engages with planetary gears by manufacturing the epicycle gear reduction mechanism internal gear by resin.
Furthermore, this overrunning clutch has a structure wherein the rotational force is conveyed when the rollers bite, in the small narrow direction, into the wedge-shaped space formed between the cam-shaped groove set on the inner circumference of the bracket which is the fixing side of the clutch outer member and inclined circumferentially and the outer circumference of the internal gear of the epicycle gear reduction mechanism that is the clutch inner member. Therefore, when the starter overruns, the internal gear that acts as the clutch inner members is rotated at a high speed, and since these are made of metal and heavy, the inertia energy during rotation is large. If the engine is rapidly changed from the overrun state to the drive state, the impact applied on the other clutch parts increases, an unbalance occurs during rotation, the device may be damaged or an abnormal noise may be heard during drive.
Furthermore, as the clutch outer member (roller cam) is mounted on the front bracket, when the starter is overrun by the engine, the ring gear (clutch inner member) rotates to absorb the rotational difference between the pinion gear rotated by the engine and the starter motor so that the overrun rotation is not conveyed to the starter motor. The rollers wear at this time because the rollers constantly contact the outer circumference of this clutch inner member.